In the prior art are known the cutting units of hydro-mechanical slot perforating machines, which include cutting tools enabling to form simultaneously two perforation slots in the production string, with the mechanism of their extension, for example, disclosed in patents RU 2249678 C2, IPC E21B 43/112, Apr. 10, 2005, RU 2371569 C1, IPC E21B 43/112, Oct. 27, 2009, RU 86654 U1, IPC E21B 43/112, Sep. 10, 2009, RU 2348797 C1, IPC E21B 43/112, Mar. 10, 2009. At that the size of cutting tools used in the mentioned designs of the cutting units approaches the diameter of the perforator's casing that allows creating perforations slots of a considerable depth.
The disadvantage of multiple-cutting units is the use of cutting tools extension mechanisms therein, envisaging the presence of a significant distance between the cutting tools in a working position, which conditions a significant height difference of the perforating slots formed simultaneously.
Known is a cutting unit of hydromechanical slot-type perforator disclosed in the patent for utility model RU 100802 U1, IPC E21B 43/112, Dec. 27, 2010, which eliminates the mentioned disadvantage. It is the closest to the present invention and is further referred to as a ‘prototype’.
The cutting unit of hydromechanical slot-type perforator of the prototype includes a retractable blades mounted on the axes of the upper and lower holders, installed inside the perforator's casing by means of the fingers, with that the upper holder is mounted on the plunger and the lower holder is secured to the housing, in addition, holders are made flat and located in the same plane with the possibility of deviations in opposite directions at translational impact of the plunger, in addition, working surfaces of the holders interacting with each other are performed at the ends of the holders, rounded, and the lower holder is additionally provided with a supporting surface with the possibility of exposure to the lower spring anchor through the washer, while the lower spring is located in the glass—the tensioner.
Cutting tools of the device, according to the prototype, are mounted at the holders close enough to each other. Advancing in opposite directions during the opposite movement and interaction of the holders, cutting tools perform back-to-radial displacement, and, taking up the operating position, turn out to be approximately at the same level relative to the vertical axis of the perforator. This ensures that the production casing opening with simultaneous formation of two perforating slots with a minimum height difference between them.
The disadvantage of the cutting unit according to the prototype is lack of an effective mechanism to bring the telescoping parts in the initial (transport) position after perforation as well as lack of restraint and fixing devices. Thus, the prototype does not provide any means for the return of the lower cutting disc in the transport position and for fixing it in such position. The upper cutting disc, which rises in the holder together with the piston under conditions of reducing operating pressure, takes up the initial position under the force of its own weight. However, the prototype does not provide the means for holding the top cutting disc in the perforator's housing during its transportation. Given the design features of the cutting unit according to the prototype, it can lead to spontaneous extension of cutting discs out of the case during transportation of the perforator and when it is lowered into the borehole, as well as to inability to remove the device from the well after perforation. In addition, the spontaneous extension of the cutting disc out of the body can cause damage and injury to personnel working with the device.